In general, an F-T reaction process is a key process of such as coal-to-liquids (coal indirect liquefaction system, CTL), gas-to-liquids (GTL), and X-to-liquids (XTL) in which oils are produced by gasifying biomass such as wood and various materials such as wastes.
Here, a ratio of hydrogen and carbon monoxide (H2/CO) that are generated in the gasification of CTL, GTL and XTL processes may be variously distributed depending on raw materials. When a solid such as coal, petroleum coke, heavy residues and biomass such as wood is used as a raw material, the content thereof is about 0.6 to about 1.2, and when a gas such as natural gas and process waste gas is used as a raw material, the content thereof is 1.2 to 2.0.
In the F-T reaction process, a synthetic gas (CO+H2) is incorporated into a reactor and reacts with a catalyst contained in a body of the reactor to produce a liquid synthetic material.
At this time, the catalyst used for the F-T reactor is generally an iron (Fe) or cobalt (Co) catalyst. The type of catalyst used for the F-T reactor depends on a ratio of the synthetic gas (H2/CO) incorporated into the reactor.
The Fe catalyst can be used in a wide H2/CO ratio range of 0.6 to 3.5 since the components contained in the catalyst induce a water gas shift reaction to convert CO into hydrogen. However, the Fe catalyst has lower activity than the Co catalyst. In order to impart a high activity to the Fe catalyst, reaction temperature and pressure are inevitably increased and, as a result, the lifespan of catalyst is shortened.
On the other hand, the cobalt catalyst has a high activity, thus having low reaction temperature and pressure, as compared to the Fe catalyst. Unless the H2/CO ratio of the cobalt catalyst is maintained at 1.8 to 2.0, inactivation of the catalyst is accelerated and the lifespan of catalyst is shortened. Accordingly, when the Co catalyst is for coal liquation process, a H2/CO ratio of synthetic gas incorporated into the F-T reactor should be maintained at 1.8 to 2.0 by adhering a hydrogen gas reactor to the front surface of the F-T reactor. In addition, the Co catalyst disadvantageously undergoes rapid deterioration in reaction activity, although a small amount of impurity such as H2S is contained in the synthetic gas, thus being unsuitable for application to the synthetic gas produced from coals.
As such, each of Fe and Co catalysts has advantages and disadvantages. For this reason, there is a need for development of combination of reaction process to supplement advantages and disadvantages and improve efficiency.